From 43dfe54ce017c8d37eaec480a2f13a492bbc4203 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton@redhat.com>
Date: Thu, 25 Feb 2021 14:24:14 +0100
Subject: [PATCH 2/2] [PATCH][lld] Import compact_unwind_encoding.h from
 libunwind

This avoids an implicit cross package dependency
---
 lld/include/mach-o/compact_unwind_encoding.h | 477 +++++++++++++++++++++++++++
 1 file changed, 477 insertions(+)
 create mode 100644 lld/include/mach-o/compact_unwind_encoding.h

diff --git a/lld/include/mach-o/compact_unwind_encoding.h b/lld/include/mach-o/compact_unwind_encoding.h
new file mode 100644
index 0000000..5301b10
--- /dev/null
+++ b/lld/include/mach-o/compact_unwind_encoding.h
@@ -0,0 +1,477 @@
+//===------------------ mach-o/compact_unwind_encoding.h ------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//
+// Darwin's alternative to DWARF based unwind encodings.
+//
+//===----------------------------------------------------------------------===//
+
+
+#ifndef __COMPACT_UNWIND_ENCODING__
+#define __COMPACT_UNWIND_ENCODING__
+
+#include <stdint.h>
+
+//
+// Compilers can emit standard DWARF FDEs in the __TEXT,__eh_frame section
+// of object files. Or compilers can emit compact unwind information in
+// the __LD,__compact_unwind section.
+//
+// When the linker creates a final linked image, it will create a
+// __TEXT,__unwind_info section.  This section is a small and fast way for the
+// runtime to access unwind info for any given function.  If the compiler
+// emitted compact unwind info for the function, that compact unwind info will
+// be encoded in the __TEXT,__unwind_info section. If the compiler emitted
+// DWARF unwind info, the __TEXT,__unwind_info section will contain the offset
+// of the FDE in the __TEXT,__eh_frame section in the final linked image.
+//
+// Note: Previously, the linker would transform some DWARF unwind infos into
+//       compact unwind info.  But that is fragile and no longer done.
+
+
+//
+// The compact unwind endoding is a 32-bit value which encoded in an
+// architecture specific way, which registers to restore from where, and how
+// to unwind out of the function.
+//
+typedef uint32_t compact_unwind_encoding_t;
+
+
+// architecture independent bits
+enum {
+    UNWIND_IS_NOT_FUNCTION_START           = 0x80000000,
+    UNWIND_HAS_LSDA                        = 0x40000000,
+    UNWIND_PERSONALITY_MASK                = 0x30000000,
+};
+
+
+
+
+//
+// x86
+//
+// 1-bit: start
+// 1-bit: has lsda
+// 2-bit: personality index
+//
+// 4-bits: 0=old, 1=ebp based, 2=stack-imm, 3=stack-ind, 4=DWARF
+//  ebp based:
+//        15-bits (5*3-bits per reg) register permutation
+//        8-bits for stack offset
+//  frameless:
+//        8-bits stack size
+//        3-bits stack adjust
+//        3-bits register count
+//        10-bits register permutation
+//
+enum {
+    UNWIND_X86_MODE_MASK                         = 0x0F000000,
+    UNWIND_X86_MODE_EBP_FRAME                    = 0x01000000,
+    UNWIND_X86_MODE_STACK_IMMD                   = 0x02000000,
+    UNWIND_X86_MODE_STACK_IND                    = 0x03000000,
+    UNWIND_X86_MODE_DWARF                        = 0x04000000,
+
+    UNWIND_X86_EBP_FRAME_REGISTERS               = 0x00007FFF,
+    UNWIND_X86_EBP_FRAME_OFFSET                  = 0x00FF0000,
+
+    UNWIND_X86_FRAMELESS_STACK_SIZE              = 0x00FF0000,
+    UNWIND_X86_FRAMELESS_STACK_ADJUST            = 0x0000E000,
+    UNWIND_X86_FRAMELESS_STACK_REG_COUNT         = 0x00001C00,
+    UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION   = 0x000003FF,
+
+    UNWIND_X86_DWARF_SECTION_OFFSET              = 0x00FFFFFF,
+};
+
+enum {
+    UNWIND_X86_REG_NONE     = 0,
+    UNWIND_X86_REG_EBX      = 1,
+    UNWIND_X86_REG_ECX      = 2,
+    UNWIND_X86_REG_EDX      = 3,
+    UNWIND_X86_REG_EDI      = 4,
+    UNWIND_X86_REG_ESI      = 5,
+    UNWIND_X86_REG_EBP      = 6,
+};
+
+//
+// For x86 there are four modes for the compact unwind encoding:
+// UNWIND_X86_MODE_EBP_FRAME:
+//    EBP based frame where EBP is push on stack immediately after return address,
+//    then ESP is moved to EBP. Thus, to unwind ESP is restored with the current
+//    EPB value, then EBP is restored by popping off the stack, and the return
+//    is done by popping the stack once more into the pc.
+//    All non-volatile registers that need to be restored must have been saved
+//    in a small range in the stack that starts EBP-4 to EBP-1020.  The offset/4
+//    is encoded in the UNWIND_X86_EBP_FRAME_OFFSET bits.  The registers saved
+//    are encoded in the UNWIND_X86_EBP_FRAME_REGISTERS bits as five 3-bit entries.
+//    Each entry contains which register to restore.
+// UNWIND_X86_MODE_STACK_IMMD:
+//    A "frameless" (EBP not used as frame pointer) function with a small 
+//    constant stack size.  To return, a constant (encoded in the compact
+//    unwind encoding) is added to the ESP. Then the return is done by
+//    popping the stack into the pc.
+//    All non-volatile registers that need to be restored must have been saved
+//    on the stack immediately after the return address.  The stack_size/4 is
+//    encoded in the UNWIND_X86_FRAMELESS_STACK_SIZE (max stack size is 1024).
+//    The number of registers saved is encoded in UNWIND_X86_FRAMELESS_STACK_REG_COUNT.
+//    UNWIND_X86_FRAMELESS_STACK_REG_PERMUTATION constains which registers were
+//    saved and their order.
+// UNWIND_X86_MODE_STACK_IND:
+//    A "frameless" (EBP not used as frame pointer) function large constant 
+//    stack size.  This case is like the previous, except the stack size is too
+//    large to encode in the compact unwind encoding.  Instead it requires that 
+//    the function contains "subl $nnnnnnnn,ESP" in its prolog.  The compact 
+//    encoding contains the offset to the nnnnnnnn value in the function in
+//    UNWIND_X86_FRAMELESS_STACK_SIZE.  
+// UNWIND_X86_MODE_DWARF:
+//    No compact unwind encoding is available.  Instead the low 24-bits of the
+//    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
+//    This mode is never used in object files.  It is only generated by the 
+//    linker in final linked images which have only DWARF unwind info for a
+//    function.
+//
+// The permutation encoding is a Lehmer code sequence encoded into a
+// single variable-base number so we can encode the ordering of up to
+// six registers in a 10-bit space.
+//
+// The following is the algorithm used to create the permutation encoding used
+// with frameless stacks.  It is passed the number of registers to be saved and
+// an array of the register numbers saved.
+//
+//uint32_t permute_encode(uint32_t registerCount, const uint32_t registers[6])
+//{
+//    uint32_t renumregs[6];
+//    for (int i=6-registerCount; i < 6; ++i) {
+//        int countless = 0;
+//        for (int j=6-registerCount; j < i; ++j) {
+//            if ( registers[j] < registers[i] )
+//                ++countless;
+//        }
+//        renumregs[i] = registers[i] - countless -1;
+//    }
+//    uint32_t permutationEncoding = 0;
+//    switch ( registerCount ) {
+//        case 6:
+//            permutationEncoding |= (120*renumregs[0] + 24*renumregs[1]
+//                                    + 6*renumregs[2] + 2*renumregs[3]
+//                                      + renumregs[4]);
+//            break;
+//        case 5:
+//            permutationEncoding |= (120*renumregs[1] + 24*renumregs[2]
+//                                    + 6*renumregs[3] + 2*renumregs[4]
+//                                      + renumregs[5]);
+//            break;
+//        case 4:
+//            permutationEncoding |= (60*renumregs[2] + 12*renumregs[3]
+//                                   + 3*renumregs[4] + renumregs[5]);
+//            break;
+//        case 3:
+//            permutationEncoding |= (20*renumregs[3] + 4*renumregs[4]
+//                                     + renumregs[5]);
+//            break;
+//        case 2:
+//            permutationEncoding |= (5*renumregs[4] + renumregs[5]);
+//            break;
+//        case 1:
+//            permutationEncoding |= (renumregs[5]);
+//            break;
+//    }
+//    return permutationEncoding;
+//}
+//
+
+
+
+
+//
+// x86_64
+//
+// 1-bit: start
+// 1-bit: has lsda
+// 2-bit: personality index
+//
+// 4-bits: 0=old, 1=rbp based, 2=stack-imm, 3=stack-ind, 4=DWARF
+//  rbp based:
+//        15-bits (5*3-bits per reg) register permutation
+//        8-bits for stack offset
+//  frameless:
+//        8-bits stack size
+//        3-bits stack adjust
+//        3-bits register count
+//        10-bits register permutation
+//
+enum {
+    UNWIND_X86_64_MODE_MASK                         = 0x0F000000,
+    UNWIND_X86_64_MODE_RBP_FRAME                    = 0x01000000,
+    UNWIND_X86_64_MODE_STACK_IMMD                   = 0x02000000,
+    UNWIND_X86_64_MODE_STACK_IND                    = 0x03000000,
+    UNWIND_X86_64_MODE_DWARF                        = 0x04000000,
+
+    UNWIND_X86_64_RBP_FRAME_REGISTERS               = 0x00007FFF,
+    UNWIND_X86_64_RBP_FRAME_OFFSET                  = 0x00FF0000,
+
+    UNWIND_X86_64_FRAMELESS_STACK_SIZE              = 0x00FF0000,
+    UNWIND_X86_64_FRAMELESS_STACK_ADJUST            = 0x0000E000,
+    UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT         = 0x00001C00,
+    UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION   = 0x000003FF,
+
+    UNWIND_X86_64_DWARF_SECTION_OFFSET              = 0x00FFFFFF,
+};
+
+enum {
+    UNWIND_X86_64_REG_NONE       = 0,
+    UNWIND_X86_64_REG_RBX        = 1,
+    UNWIND_X86_64_REG_R12        = 2,
+    UNWIND_X86_64_REG_R13        = 3,
+    UNWIND_X86_64_REG_R14        = 4,
+    UNWIND_X86_64_REG_R15        = 5,
+    UNWIND_X86_64_REG_RBP        = 6,
+};
+//
+// For x86_64 there are four modes for the compact unwind encoding:
+// UNWIND_X86_64_MODE_RBP_FRAME:
+//    RBP based frame where RBP is push on stack immediately after return address,
+//    then RSP is moved to RBP. Thus, to unwind RSP is restored with the current 
+//    EPB value, then RBP is restored by popping off the stack, and the return 
+//    is done by popping the stack once more into the pc.
+//    All non-volatile registers that need to be restored must have been saved
+//    in a small range in the stack that starts RBP-8 to RBP-2040.  The offset/8 
+//    is encoded in the UNWIND_X86_64_RBP_FRAME_OFFSET bits.  The registers saved
+//    are encoded in the UNWIND_X86_64_RBP_FRAME_REGISTERS bits as five 3-bit entries.
+//    Each entry contains which register to restore.  
+// UNWIND_X86_64_MODE_STACK_IMMD:
+//    A "frameless" (RBP not used as frame pointer) function with a small 
+//    constant stack size.  To return, a constant (encoded in the compact 
+//    unwind encoding) is added to the RSP. Then the return is done by 
+//    popping the stack into the pc.
+//    All non-volatile registers that need to be restored must have been saved
+//    on the stack immediately after the return address.  The stack_size/8 is
+//    encoded in the UNWIND_X86_64_FRAMELESS_STACK_SIZE (max stack size is 2048).
+//    The number of registers saved is encoded in UNWIND_X86_64_FRAMELESS_STACK_REG_COUNT.
+//    UNWIND_X86_64_FRAMELESS_STACK_REG_PERMUTATION constains which registers were
+//    saved and their order.  
+// UNWIND_X86_64_MODE_STACK_IND:
+//    A "frameless" (RBP not used as frame pointer) function large constant 
+//    stack size.  This case is like the previous, except the stack size is too
+//    large to encode in the compact unwind encoding.  Instead it requires that 
+//    the function contains "subq $nnnnnnnn,RSP" in its prolog.  The compact 
+//    encoding contains the offset to the nnnnnnnn value in the function in
+//    UNWIND_X86_64_FRAMELESS_STACK_SIZE.  
+// UNWIND_X86_64_MODE_DWARF:
+//    No compact unwind encoding is available.  Instead the low 24-bits of the
+//    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
+//    This mode is never used in object files.  It is only generated by the 
+//    linker in final linked images which have only DWARF unwind info for a
+//    function.
+//
+
+
+// ARM64
+//
+// 1-bit: start
+// 1-bit: has lsda
+// 2-bit: personality index
+//
+// 4-bits: 4=frame-based, 3=DWARF, 2=frameless
+//  frameless:
+//        12-bits of stack size
+//  frame-based:
+//        4-bits D reg pairs saved
+//        5-bits X reg pairs saved
+//  DWARF:
+//        24-bits offset of DWARF FDE in __eh_frame section
+//
+enum {
+    UNWIND_ARM64_MODE_MASK                     = 0x0F000000,
+    UNWIND_ARM64_MODE_FRAMELESS                = 0x02000000,
+    UNWIND_ARM64_MODE_DWARF                    = 0x03000000,
+    UNWIND_ARM64_MODE_FRAME                    = 0x04000000,
+
+    UNWIND_ARM64_FRAME_X19_X20_PAIR            = 0x00000001,
+    UNWIND_ARM64_FRAME_X21_X22_PAIR            = 0x00000002,
+    UNWIND_ARM64_FRAME_X23_X24_PAIR            = 0x00000004,
+    UNWIND_ARM64_FRAME_X25_X26_PAIR            = 0x00000008,
+    UNWIND_ARM64_FRAME_X27_X28_PAIR            = 0x00000010,
+    UNWIND_ARM64_FRAME_D8_D9_PAIR              = 0x00000100,
+    UNWIND_ARM64_FRAME_D10_D11_PAIR            = 0x00000200,
+    UNWIND_ARM64_FRAME_D12_D13_PAIR            = 0x00000400,
+    UNWIND_ARM64_FRAME_D14_D15_PAIR            = 0x00000800,
+
+    UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK     = 0x00FFF000,
+    UNWIND_ARM64_DWARF_SECTION_OFFSET          = 0x00FFFFFF,
+};
+// For arm64 there are three modes for the compact unwind encoding:
+// UNWIND_ARM64_MODE_FRAME:
+//    This is a standard arm64 prolog where FP/LR are immediately pushed on the
+//    stack, then SP is copied to FP. If there are any non-volatile registers
+//    saved, then are copied into the stack frame in pairs in a contiguous
+//    range right below the saved FP/LR pair.  Any subset of the five X pairs 
+//    and four D pairs can be saved, but the memory layout must be in register
+//    number order.  
+// UNWIND_ARM64_MODE_FRAMELESS:
+//    A "frameless" leaf function, where FP/LR are not saved. The return address 
+//    remains in LR throughout the function. If any non-volatile registers
+//    are saved, they must be pushed onto the stack before any stack space is
+//    allocated for local variables.  The stack sized (including any saved
+//    non-volatile registers) divided by 16 is encoded in the bits 
+//    UNWIND_ARM64_FRAMELESS_STACK_SIZE_MASK.
+// UNWIND_ARM64_MODE_DWARF:
+//    No compact unwind encoding is available.  Instead the low 24-bits of the
+//    compact encoding is the offset of the DWARF FDE in the __eh_frame section.
+//    This mode is never used in object files.  It is only generated by the 
+//    linker in final linked images which have only DWARF unwind info for a
+//    function.
+//
+
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+//  Relocatable Object Files: __LD,__compact_unwind
+//
+////////////////////////////////////////////////////////////////////////////////
+
+//
+// A compiler can generated compact unwind information for a function by adding
+// a "row" to the __LD,__compact_unwind section.  This section has the 
+// S_ATTR_DEBUG bit set, so the section will be ignored by older linkers. 
+// It is removed by the new linker, so never ends up in final executables. 
+// This section is a table, initially with one row per function (that needs 
+// unwind info).  The table columns and some conceptual entries are:
+//
+//     range-start               pointer to start of function/range
+//     range-length              
+//     compact-unwind-encoding   32-bit encoding  
+//     personality-function      or zero if no personality function
+//     lsda                      or zero if no LSDA data
+//
+// The length and encoding fields are 32-bits.  The other are all pointer sized. 
+//
+// In x86_64 assembly, these entry would look like:
+//
+//     .section __LD,__compact_unwind,regular,debug
+//
+//     #compact unwind for _foo
+//     .quad    _foo
+//     .set     L1,LfooEnd-_foo
+//     .long    L1
+//     .long    0x01010001
+//     .quad    0
+//     .quad    0
+//
+//     #compact unwind for _bar
+//     .quad    _bar
+//     .set     L2,LbarEnd-_bar
+//     .long    L2
+//     .long    0x01020011
+//     .quad    __gxx_personality
+//     .quad    except_tab1
+//
+//
+// Notes: There is no need for any labels in the the __compact_unwind section.  
+//        The use of the .set directive is to force the evaluation of the 
+//        range-length at assembly time, instead of generating relocations.
+//
+// To support future compiler optimizations where which non-volatile registers 
+// are saved changes within a function (e.g. delay saving non-volatiles until
+// necessary), there can by multiple lines in the __compact_unwind table for one
+// function, each with a different (non-overlapping) range and each with 
+// different compact unwind encodings that correspond to the non-volatiles 
+// saved at that range of the function.
+//
+// If a particular function is so wacky that there is no compact unwind way
+// to encode it, then the compiler can emit traditional DWARF unwind info.  
+// The runtime will use which ever is available.
+//
+// Runtime support for compact unwind encodings are only available on 10.6 
+// and later.  So, the compiler should not generate it when targeting pre-10.6. 
+
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+//
+//  Final Linked Images: __TEXT,__unwind_info
+//
+////////////////////////////////////////////////////////////////////////////////
+
+//
+// The __TEXT,__unwind_info section is laid out for an efficient two level lookup.
+// The header of the section contains a coarse index that maps function address
+// to the page (4096 byte block) containing the unwind info for that function.  
+//
+
+#define UNWIND_SECTION_VERSION 1
+struct unwind_info_section_header
+{
+    uint32_t    version;            // UNWIND_SECTION_VERSION
+    uint32_t    commonEncodingsArraySectionOffset;
+    uint32_t    commonEncodingsArrayCount;
+    uint32_t    personalityArraySectionOffset;
+    uint32_t    personalityArrayCount;
+    uint32_t    indexSectionOffset;
+    uint32_t    indexCount;
+    // compact_unwind_encoding_t[]
+    // uint32_t personalities[]
+    // unwind_info_section_header_index_entry[]
+    // unwind_info_section_header_lsda_index_entry[]
+};
+
+struct unwind_info_section_header_index_entry
+{
+    uint32_t        functionOffset;
+    uint32_t        secondLevelPagesSectionOffset;  // section offset to start of regular or compress page
+    uint32_t        lsdaIndexArraySectionOffset;    // section offset to start of lsda_index array for this range
+};
+
+struct unwind_info_section_header_lsda_index_entry
+{
+    uint32_t        functionOffset;
+    uint32_t        lsdaOffset;
+};
+
+//
+// There are two kinds of second level index pages: regular and compressed.
+// A compressed page can hold up to 1021 entries, but it cannot be used
+// if too many different encoding types are used.  The regular page holds
+// 511 entries.
+//
+
+struct unwind_info_regular_second_level_entry
+{
+    uint32_t                    functionOffset;
+    compact_unwind_encoding_t    encoding;
+};
+
+#define UNWIND_SECOND_LEVEL_REGULAR 2
+struct unwind_info_regular_second_level_page_header
+{
+    uint32_t    kind;    // UNWIND_SECOND_LEVEL_REGULAR
+    uint16_t    entryPageOffset;
+    uint16_t    entryCount;
+    // entry array
+};
+
+#define UNWIND_SECOND_LEVEL_COMPRESSED 3
+struct unwind_info_compressed_second_level_page_header
+{
+    uint32_t    kind;    // UNWIND_SECOND_LEVEL_COMPRESSED
+    uint16_t    entryPageOffset;
+    uint16_t    entryCount;
+    uint16_t    encodingsPageOffset;
+    uint16_t    encodingsCount;
+    // 32-bit entry array
+    // encodings array
+};
+
+#define UNWIND_INFO_COMPRESSED_ENTRY_FUNC_OFFSET(entry)            (entry & 0x00FFFFFF)
+#define UNWIND_INFO_COMPRESSED_ENTRY_ENCODING_INDEX(entry)        ((entry >> 24) & 0xFF)
+
+
+
+#endif
+
-- 
1.8.3.1

